1. Field of the Invention
The present invention is directed generally to a planar optical display, and, more particularly, to a high contrast front projection display panel and a method of making a high contrast front projection display panel.
2. Description of the Background
Video display screens typically use cathode ray tubes (CRTs) for projecting an image onto the outlet face of the screen. A typical screen of this type has a width to height ratio of 4:3 with 525 vertical lines of resolution. An electron beam must be scanned both horizontally and vertically on the screen to form a number of pixels, which collectively form the image. Conventional cathode ray tubes have a practical limit in size and are relatively deep to accommodate the required electron gun. Larger screen televisions are available which typically include various forms of image projection for increasing the screen image size. However, such screens may experience limited viewing angle, limited resolution, decreased brightness, and decreased contrast, particularly in display screens using front projections. This is, in part, due to the use of white screens to allow the screen to reflect the front projection back to the user. Thus, because the screen is white, the darkest black level that can be displayed is xe2x80x9cscreen whitexe2x80x9d, the color of the screen when the projection is off, due to the fact that black light cannot be projected. Consequently, the projection must be either on, or off, to produce white, or black, respectively. Thus, where black is viewed on a front screen projection system, the viewer is actually seeing the white of the background, i.e the absence of projected light, which the human eye sees as black in the context of the white light projected elsewhere on the background, meaning that the presence of the optical spectrum projected onto the white background forms a xe2x80x9cwhiter than whitexe2x80x9d color, which the eye sees as white. This is the reason that a room must be darkened in order for a viewer to see black on a front projection screen.
Optical panels can be created using a plurality of stacked waveguides, and may be rendered black using at least one black cladding layer between transparent cores of the waveguides. The cladding layers disclosed therein have a lower index of refraction than the waveguide cores for effectuating substantial internal reflection of the image light channeled through the cores, and thereby improve contrast, i.e. thereby improve the appearance of black images on a screen. Such optical panel displays have typically been operated in a rear projection mode.
Therefore, the need exists for a display panel that allows for front projection, while also providing the appearance of a black screen to improve viewing contrast and to eliminate the need to dim lights in order to allow a viewer to see black images.
The present invention is directed to an optical display panel which provides improved viewing contrast for front projection applications. The optical panel includes a plurality of stacked optical waveguides, wherein each waveguide has a back face and an outlet face at opposing ends of each waveguide, and wherein each waveguide is formed of a core between an opposing pair of cladding layers, and at least one reflector connected to the back face of at least one waveguide, wherein the at least one reflector receives image light incident through at least one waveguide from the outlet face, and wherein the at least one reflector redirects the image light back through the at least one waveguide out of the outlet face. In the preferred embodiment, the outlet face is rendered black by inclusion of black within or between cladding layers.
The present invention is also directed to a method of producing a stacked optical waveguide panel for front projection applications. In one preferred embodiment of the present invention, clear strips of plastic, which are preferably approximately xc2xexe2x80x3 by 40xe2x80x3, and approximately {fraction (20/1000)}xe2x80x3 thick, are stacked, with a thin double sided black adhesive strip between each plastic strip. The stack may include 2000-3000 of the strips. The strip stack is then pressed under high pressure to eliminate air bubbles and improve adhesion. Another method includes coating a plurality of glass sheets on each of two faces with a first substance having an index of refraction lower than that of the glass sheets, placing a first coated glass sheet into a trough sized slightly larger than the first coated glass sheet, filling the trough with a thermally curing black epoxy, stacking the plurality of coated glass sheets within the filled trough, curing the epoxy, forming, at two opposite ends of the stack, a back face and an outlet face, and connecting at least one reflector to the back face.
The optical display panel for front projection applications solves problems experienced in the prior art by providing a display panel that allows for front projection, while also providing the appearance of a black screen to improve viewing contrast and to eliminate the need to dim lights in order to allow a viewer to see black images.